This invention relates to a new and improved motorized shunt trip operator for a bolted pressure contact switch, and particularly to an improved electrical motor assembly for actuating the switch.
Fused load-break switches are frequently used as service entrance equipment and in other relatively high current applications. Typically, multiple-pole switches of this kind may be required to interrupt currents of 400 to 20,000 amperes. It is critcally important that the contacts of these switches open and close rapidly to minimize arcing and thereby avoid pitting and deterioration of the switch contacts. Most switches of this kind are provided with a latching mechanism for each pole of the switch to secure the contacts in closed position and prevent any accidental opening of the switch due to external shocks or other factors. The switch blades are relatively heavy and the mechanical forces involved in opening and closing operations are often substantial.
In many applications, load-break switches must include provision for opening and closing of the switches from remote locations. The usual solution of this problem has been the provision of motor-operated switch mechanisms. Gear motors are often employed for this purpose but are slow in operation and delay contact separation by one-half second or more after the initial fault signal. In comparison, a spring-operated switch may effect contact separation in about 1/10 second.
A motor employed directly to load the springs of a spring-operated switch mechanism would have to be quite large to provide the force necessary for rapid switch operation. Such a motor would add to the overall weight as well as the expense of a given switch installation. In addition, a separate reset cycle may have to be initiated after each actuation of the motor in order to position the operating parts of the motor assembly for subsequent actuation to open or close the switch.
Several other problems may be encountered in the operation of heavy-duty switches, particularly where remote actuation is required. If the switches are constructed for manual as well as motor operation, there is a risk of injury to any personnel near the switches if the handle for manual operation is interlocked to the motor drive. Such construction may well be found where a motor assist is provided for only the opening or only the closing operation, with the other being accomplished manually. But even regardless of safety, the force necessary for manual operation of large switches of this type may make it quite difficult if not impossible for certain individuals to operate the switch. Those persons unfamiliar with such a switch, which may be concealed within a protective housing, will have further difficulty if the handle position is not readily indicative of the condition of the switch, i.e., whether it is open or closed. Similarly, even when the protective housing is opened, the switch contacts are generally concealed behind an opaque barrier or shield which thereby deprives the operator of the most obvious indication of the condition of the switch.